Software

Arrow

Developer

Migrating EJB 2.1 Entity and Session Beans to EJB 3.0

The nuts and bolts

Table 2. EntityManager Class

EntityManager Method Description
persist Creates an entity bean instance.
createNamedQuery Creates a named query.
find Finds an entity bean instance.
createQuery Creates an EJBQL query.
remove Removes an entity bean instance.

In a session bean client class for EJB 3.0 entity bean, the EntityManager reference is obtained with the @Resource annotation:

@Resource
private EntityManager em;

An entity bean instance is created with the persist() method of the EntityManager class:

CatalogBean catalogBean=new CatalogBean(catalogId);
em.persist(catalogBean);

An entity bean instance is obtained with the find() method:

CatalogBean catalogBean=(CatalogBean)em.find("CatalogBean", catalogId);

A finder method may be defined corresponding to the named query findByJournal in the entity bean POJO class. In the finder method a Query object is obtained with the createNamedQuery method:

Query query=em.createNamedQuery("findByJournal");

Set the Query object parameters with the setParameter method:

query.setParameter(0, journal);

Obtain a Collection of the CatalogBean with the getResultList() method. If a Query object returns a single result, the getSingleResult() is used:

java.util.Collection catalogBeanCollection=(CatalogBean)query.getResultList();

An entity bean instance is removed with the remove() method of the EntityManager class:

CatalogBean catalogBean;
em.remove(catalogBean);

The client class for the EJB 3.0 entity bean is listed in Listing 9.

Listing 9. CatalogClient. EJB 3.0 Client Class

import javax.ejb.Stateless;
import javax.ejb.Resource;
import javax.persistence.EntityManager;
import javax.persistence.Query;

@Stateless
@Local
public class CatalogClient implements CatalogLocal {
    @Resource
    private EntityManager em;

    public void create(String catalogId) {
        CatalogBean catalogBean=new CatalogBean(catalogId);
        em.persist(catalogBean);
    }

    public CatalogBean findByPrimaryKey(String catalogId) {
        return (CatalogBean)em.find("CatalogBean", catalogId);
    }

    public java.util.Collection findByJournal(String journal) {
        Query query=em.createNamedQuery("findByJournal");
        query.setParameter(0, journal);
        return (CatalogBean)query.getResultList();
    }

    public void remove(CatalogBean catalogBean) {
        em.remove(catalogBean);
    }
}

Sponsored: Go beyond APM with real-time IT operations analytics

Next page: Summary